Accidental reverse flow from a sanitary system into a water supply system is of particular concern in view of its likely serious impact on the public welfare, and the various health authorities are continually urging the adoption of more effective legislation and building codes with an eye toward the complete elimination of this potentially serious problem. Generally, water and sanitary systems can be isolated from each other by spacial separation. However, the construction of water closets does not generally permit effective separation.
The reservoir tank of a water closet is a particularly susceptible source for this undesirable reverse flow. For example, reverse flow can be occasioned within the reservoir tank if the water supply line which feeds the tank should develop a leak. In such a situation the resulting pressure reduction in the water supply line can effect a siphoning of the water from the reservoir tank into the water supply line--i.e., the unacceptable reverse flow.
A number of prior known ball cock arrangements have been employed over the years to alleviate the possibilty of reverse flow when the feed line develops a leak. One such approach has been to provide a ball cock valve that would remain closed irrespective of the line pressure in the water line feeding the reservoir tank. Such a result is achieved by the balance valve mechanism disclosed in my prior U.S. Pat. No. 4,479,631, issued Oct. 30, 1984 for a "Hydraulically Balanced Valve Mechanism." According to that arrangement, which also provides a number of other desired features as a result of its balanced operation, reverse flow is obviated so long as the toilet is not flushed and the level of the fluid in the reservoir remains sufficiently high that the reservoir filling cycle is not initiated.
However, even with that favorable design reverse flow could be occasioned if the tiolet were flushed before the leak in the supply line could be corrected. In that situation, the flush cycle would lower the water in the reservoir tank, allowing the ball cock to open for the admission of replenishing water to the reservoir tank. With the ball cock thus opened, a reduction in the line pressure within the supply line can initiate a siphoning of the water from the reservoir tank into the supply line.